diff --git a/lapi.c b/lapi.c
index 3e24781e..184b8dd7 100644
--- a/lapi.c
+++ b/lapi.c
@@ -563,6 +563,7 @@ LUA_API void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n) {
     while (n--) {
       setobj2n(L, &cl->upvalue[n], s2v(L->top + n));
       /* does not need barrier because closure is white */
+      lua_assert(iswhite(cl));
     }
     setclCvalue(L, s2v(L->top), cl);
     api_incr_top(L);
diff --git a/lundump.c b/lundump.c
index 4243678a..cb124d6f 100644
--- a/lundump.c
+++ b/lundump.c
@@ -200,13 +200,20 @@ static void loadProtos (LoadState *S, Proto *f) {
 }
 
 
+/*
+** Load the upvalues for a function. The names must be filled first,
+** because the filling of the other fields can raise read errors and
+** the creation of the error message can call an emergency collection;
+** in that case all prototypes must be consistent for the GC.
+*/
 static void loadUpvalues (LoadState *S, Proto *f) {
   int i, n;
   n = loadInt(S);
   f->upvalues = luaM_newvectorchecked(S->L, n, Upvaldesc);
   f->sizeupvalues = n;
-  for (i = 0; i < n; i++) {
+  for (i = 0; i < n; i++)  /* make array valid for GC */
     f->upvalues[i].name = NULL;
+  for (i = 0; i < n; i++) {  /* following calls can raise errors */
     f->upvalues[i].instack = loadByte(S);
     f->upvalues[i].idx = loadByte(S);
     f->upvalues[i].kind = loadByte(S);
diff --git a/testes/calls.lua b/testes/calls.lua
index 1701f155..decf4176 100644
--- a/testes/calls.lua
+++ b/testes/calls.lua
@@ -422,20 +422,30 @@ assert((function (a) return a end)() == nil)
 
 print("testing binary chunks")
 do
-  local header = string.pack("c4BBc6BBBj",
+  local header = string.pack("c4BBc6BBB",
     "\27Lua",                                  -- signature
     0x54,                                      -- version 5.4 (0x54)
     0,                                         -- format
     "\x19\x93\r\n\x1a\n",                      -- data
     4,                                         -- size of instruction
     string.packsize("j"),                      -- sizeof(lua integer)
-    string.packsize("n"),                      -- sizeof(lua number)
-    0x5678                                     -- LUAC_INT
-    -- LUAC_NUM may not have a unique binary representation (padding...)
+    string.packsize("n")                       -- sizeof(lua number)
   )
-  local c = string.dump(function () local a = 1; local b = 3; return a+b*3 end)
+  local c = string.dump(function ()
+    local a = 1; local b = 3;
+    local f = function () return a + b + _ENV.c; end    -- upvalues
+    local s1 = "a constant"
+    local s2 = "another constant"
+    return a + b * 3
+  end)
 
+  assert(assert(load(c))() == 10)
+
+  -- check header
   assert(string.sub(c, 1, #header) == header)
+  -- check LUAC_INT and LUAC_NUM
+  local ci, cn = string.unpack("jn", c, #header + 1)
+  assert(ci == 0x5678 and cn == 370.5)
 
   -- corrupted header
   for i = 1, #header do
@@ -451,7 +461,6 @@ do
     local st, msg = load(string.sub(c, 1, i))
     assert(not st and string.find(msg, "truncated"))
   end
-  assert(assert(load(c))() == 10)
 end
 
 print('OK')